High and low voltage limited power amplification system

ABSTRACT

Cascode power amplifier with voltage limiter. A power amplification system can include an input transistor having an input transistor gate configured to receive a radio-frequency (RF) signal, an input transistor source coupled to a ground voltage, and an input transistor drain. The power amplification can further include an output transistor having an output transistor drain configured to output an amplified version of the RF signal, an output transistor gate coupled to a bias voltage, and an output transistor source. The power amplification system can further include a high voltage limiter coupled between the output transistor drain and output transistor gate. The high voltage limiter can be configured to prevent a gate-drain voltage of the output transistor from exceeding a high voltage threshold.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. application Ser. No.14/829,472 filed Aug. 18, 2015, entitled “CASCODE POWER AMPLIFIER WITHVOLTAGE LIMITER,” which claims priority to U.S. Provisional ApplicationNo. 62/040,282 filed Aug. 21, 2014, entitled “METHOD AND APPARATUS FOREFFICIENTLY PROVIDING POWER IN A VARIABLE POWER TRANSMITTER,” thedisclosure of each of which is hereby expressly incorporated byreference herein in its entirety for all purposes.

BACKGROUND Field

The present disclosure generally relates to power amplifiers.

Description of the Related Art

In a cascode power amplifier, the voltage at the output is dividedbetween the various devices used in the cascode ladder, reducing thevoltage across each device to below a breakdown voltage of the device.In some implementations, each device of the cascode is biased at adifferent voltage to achieve enhanced performance. However, in mostcascode architectures, the voltage bias is only optimized at onevoltage.

SUMMARY

In accordance with some implementations, the present disclosure relatesto a power amplification system. The power amplification system includesan input transistor having an input transistor gate configured toreceive a radio-frequency (RF) signal, an input transistor sourcecoupled to a ground voltage, and an input transistor drain. The poweramplification system includes an output transistor having an outputtransistor drain configured to output an amplified version of the RFsignal, an output transistor gate coupled to a bias voltage, and anoutput transistor source. The power amplification system includes a highvoltage limiter coupled between the output transistor drain and outputtransistor gate. The high voltage limiter is configured to prevent agate-drain voltage of the output transistor from exceeding a highvoltage threshold.

In some embodiments, the high voltage limiter can include a high voltagelimiter transistor having a high voltage limiter transistor gate coupledto the output transistor drain, a high voltage limiter transistor draincoupled to the output transistor drain, and a high voltage limitertransistor source coupled to the output transistor gate.

In some embodiments, the output transistor drain can be coupled to asupply voltage via an inductor.

In some embodiments, the power amplification system can include one ormore middle transistors coupling the input transistor drain to theoutput transistor source. In some embodiments, the one or more middletransistors can include a first middle transistor having a first middletransistor gate coupled to the bias voltage and a first middletransistor drain coupled to the output transistor source.

In some embodiments, the power amplification system can include a lowvoltage limiter coupled between the supply voltage and the first middletransistor gate. The low voltage limiter can be configured to preventthe gate voltage of the first middle transistor from dropping below alow voltage threshold.

In some embodiments, the low voltage limiter can include a low voltagelimiter transistor having a low voltage limiter transistor sourcecoupled to the first middle transistor gate, a low voltage limitertransistor drain coupled to the supply voltage, and a low voltagelimiter gate coupled to a supplemental bias voltage. In someembodiments, the supplemental bias voltage can be higher than the biasvoltage.

In some embodiments, the power amplification system can include a secondmiddle transistor having a second middle transistor gate coupled to thebias voltage, a second middle transistor drain coupled to the firstmiddle transistor source, and a second middle transistor source coupledto the input transistor drain.

In some embodiments, the first middle transistor gate can be coupled tothe bias voltage via a first RC circuit including a first resistorcoupled between the first middle transistor gate and the bias voltageand a first capacitor coupled between the first middle transistor gateand the ground voltage. In some embodiments, the second middletransistor gate can be coupled to the bias voltage via a second RCcircuit including a second resistor coupled between the second middletransistor gate and the bias voltage and a second capacitor coupledbetween the first middle transistor gate and the ground voltage. In someembodiments, the first capacitor can have a first capacitance and thesecond capacitor can have a second capacitance, the second capacitancebeing larger than the first capacitance.

In some embodiments, the output transistor gate is coupled to the biasvoltage via an RC circuit including a resistor coupled between theoutput transistor gate and the bias voltage and a capacitor coupledbetween the output transistor gate and the ground voltage.

In some embodiments, the power amplification system can include an inputbias circuit disposed at the input transistor gate.

In some embodiments, the power amplification can include an output matchcircuit disposed at the output transistor drain.

In some implementations, the present disclosure relates to aradio-frequency (RF) module including a packaging substrate configuredto receive a plurality of components. The RF module includes a poweramplification system implemented on the packaging substrate. The poweramplification system includes an input transistor having an inputtransistor gate configured to receive a radio-frequency (RF) signal, aninput transistor source coupled to a ground voltage, and an inputtransistor drain. The power amplification system includes an outputtransistor having an output transistor drain configured to outputtransistor gate configured to output an amplified version of the RFsignal, an output transistor gate coupled to a bias voltage, and anoutput transistor source. The power amplification system includes a highvoltage limiter coupled between the output transistor drain and outputtransistor gate. The high voltage limiter is configured to prevent agate-drain voltage of the output transistor from exceeding a highvoltage threshold.

In some embodiments, the packaging substrate can include asilicon-on-insulator (SOI) substrate.

In some embodiments, the input transistor and output transistor can becomplementary metal-oxide semiconductor (CMOS) transistors.

In some implementations, the present disclosure relates to a wirelessdevice including a transceiver configured to generate a radio-frequency(RF) signal. The wireless device includes a front-end module (FEM) incommunication with the transceiver. The FEM includes a packagingsubstrate configured to receive a plurality of components. The FEMfurther includes a power amplification system implemented on thepackaging substrate. The power amplification system includes an inputtransistor having an input transistor gate configured to receive aradio-frequency (RF) signal, an input transistor source coupled to aground voltage, and an input transistor drain. The power amplificationsystem includes an output transistor having an output transistor drainconfigured to output transistor gate configured to output an amplifiedversion of the RF signal, an output transistor gate coupled to a biasvoltage, and an output transistor source. The power amplification systemincludes a high voltage limiter coupled between the output transistordrain and output transistor gate. The high voltage limiter is configuredto prevent a gate-drain voltage of the output transistor from exceedinga high voltage threshold. The wireless device further includes anantenna in communication with the FEM. The antenna is configured totransmit the amplified RF signal received from the power amplificationsystem.

In some embodiments, the power amplification system further includes alow voltage limiter configured to prevent a gate voltage of a transistorfrom dropping below a low voltage threshold.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an example architecture of a power amplification system.

FIG. 2 shows that, in some implementations, a power amplification systemcan include a cascode power amplifier.

FIG. 3 shows an example plot of the voltages at the drains of thetransistors of FIG. 2 over time when the amplified RF signal is greaterthan 10 volts.

FIG. 4 shows an example plot of the voltages at the drains of thetransistors of FIG. 2 over time when the amplified RF signal is below8.5 volts.

FIG. 5 shows that, in some implementations, a power amplification systemcan include multiple voltage limiters.

FIG. 6 shows a flowchart representation of a method of amplifying an RFsignal.

FIG. 7 depicts a module having one or more features as described herein.

FIG. 8 depicts a wireless device having one or more features describedherein.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The headings provided herein, if any, are for convenience only and donot necessarily affect the scope or meaning of the claimed invention.

Described herein are circuits, systems, and methods for a dynamicbiasing technique to set the gate voltages of cascode devices of a poweramplification stage. The various implementations described herein may bebeneficially used in processes where low breakdown voltages prohibit theuse of one device as the power amplification stage, for example, in CMOS(complementary metal-oxide semiconductor) and SOI (silicon-on-insulator)processes, where devices can have a low drain-source and/or gate-drainbreakdown voltage when compared to the desired output voltage levelsneeded to deliver a required amount of power.

FIG. 1 shows an example architecture of a power amplification system100. The power amplification system 100 includes a power amplifier 110with one or more transistors 111. The power amplifier 110 receives aradio-frequency (RF) signal to be amplified at an RF input (RFin)terminal 101 and yields an amplified version of the RF signal (referredto as an amplified RF signal) at an RF output (RFout) terminal 102. Thepower amplifier 110 is powered by a supply voltage (Vcc) received at asupply voltage terminal 103 and enabled or disabled by one or more biasvoltages received at one or more bias terminals 104. In particular, thebias voltages can bias one or more of the transistors 111 (e.g., tooperate the transistors 111 in an active mode).

The power amplification system 100 further includes a voltage limitationsystem 120 which limits voltages across certain components of the poweramplifier 110, e.g., the transistors 111. The voltage limitation system120 includes a high voltage limiter 121 that prevents voltages fromexceeding a high voltage threshold. For example, the high voltagelimiter 121 can prevent voltages across one or more of the transistorsfrom exceeding a breakdown voltage. The voltage limitation system 120includes a low voltage limiter 122 that prevents voltages from droppingbelow a low voltage threshold. For example, the low voltage limiter 122can prevent a gate voltage at one or more of the transistors fromdropping below a bias voltage that places the transistor in an activemode.

FIG. 2 shows that, in some implementations, a power amplification system200 can include a cascode power amplifier. The power amplificationsystem 200 includes four transistors 211-214 in a cascode topology. Eachof the transistors 211-214 (and the other transistors described herein)can be MOSFET (metal-oxide-semiconductor field-effect transistor)transistors, such as those found in typical SOI processes. In someimplementations, the transistors can be JFET (junction gate field-effecttransistor), IGFET (insulated-gate field-effect transistor), BJT(bipolar junction transistor), or other types of transistors.

The power amplification system 200 includes an input transistor 211having an input transistor gate configured to receive a radio-frequency(RF) signal, an input transistor source coupled to a ground voltage, andan input transistor drain. The power amplification system 200 furtherincludes an output transistor 214 having an output transistor drainconfigured to output an amplified version of the RF signal, an outputtransistor gate coupled to a bias voltage (Bias0), and an outputtransistor source. The output transistor drain is coupled to a supplyvoltage (Vcc) via an inductor 251.

Coupling the input transistor drain and the output transistor source areone or more middle transistors 212-213. In the implementation of FIG. 2,the power amplification system 200 includes a first middle transistor213 having a first middle transistor gate coupled to the bias voltageand a first middle transistor drain coupled to the output transistorsource and further includes a second middle transistor 212 having asecond middle transistor gate coupled to the bias voltage, a secondmiddle transistor drain coupled to the first middle transistor source,and a second middle transistor source coupled to the input transistordrain.

As mentioned above, when an RF signal is applied to the gate of theinput transistor 211, an amplified version of the RF signal is output atthe drain of the output transistor 214. In some circumstances, theamplified version of the RF signal may include high voltages (e.g.,during a positive half-cycle) such that the difference between theamplified version of the RF signal and the bias voltage applied to thegate of the output transistor would exceed a breakdown voltage of theoutput transistor 214 (e.g., approximately 3 to 4 volts). To preventsuch an occurrence, the power amplification system 200 includes a highvoltage limiter coupled between the output transistor drain and outputtransistor gate. The high voltage limiter is configured to prevent agate-drain voltage of the output transistor 214 from exceeding a highvoltage threshold, e.g., a breakdown voltage.

In the implementation of FIG. 2, the high voltage limiter is implementedas a high voltage limiter transistor 221 having a high voltage limitertransistor gate coupled to the output transistor drain, a high voltagelimiter transistor drain coupled to the output transistor drain, and ahigh voltage limiter transistor source coupled to the output transistorgate. When the voltage between the output transistor drain (the outputsignal) and the output transistor gate approaches or exceeds a highvoltage threshold, the high voltage limiter transistor 221 feeds backthe output signal to the output transistor gate and thereby provide oneof several bias sources for the output transistor gate.

As the output transistor gate is coupled to the middle transistor gates(via RC elements described further below), the fed back output signalalso provides one of several bias sources for the middle transistorgates, thereby preventing the gate-drain voltages of the middletransistors from exceeding a breakdown voltage.

As mentioned above, when an RF signal is applied to the gate of theinput transistor 211, an amplified version of the RF signal is output atthe drain of the output transistor 214. A less-amplified version of theRF signal is also present at the drain of the first middle transistor213. Similarly, an even-less-amplified version of the RF signal is alsopresent at the drain of the second middle transistor 212.

Due to the gate-drain capacitance of the first middle transistor 213,the less-amplified version of the RF signal affects the voltage at thegate of the first cascode amplifier 213. In some circumstances, thiseffect, particularly when the less-amplified version of the RF signalincludes low voltages (e.g., during a negative half-cycle), could reducethe gate voltage to such an extent that the first middle transistor 213is no longer in an active mode. To prevent such an occurrence, the poweramplification system 200 includes a low voltage limiter coupled betweenthe supply voltage and first middle transistor gate. The low voltagelimiter is configured to prevent the gate voltage of the first middletransistor 213 from dropping below a low voltage threshold.

In the implementation of FIG. 2, the low voltage limiter is implementedas a low voltage limiter transistor 231 having a low voltage limitertransistor source coupled to the first middle transistor gate, a lowvoltage limiter transistor drain coupled to the supply voltage, and alow voltage limiter gate coupled to a supplemental bias voltage (Bias1).The low voltage limiter transistor 231 feeds the supply voltage to thefirst middle transistor gate (and via the RC elements, other gates) andthereby provides one of several bias sources for the first middletransistor gate.

The output transistor gate is coupled to the bias voltage via an RCcircuit including a resistor 263 coupled between the output transistorgate and the bias voltage and a capacitor 273 coupled between the outputtransistor gate and the ground voltage. The resistor 263 and capacitor273 may be chosen to permit the amplified RF signal to pass (from thehigh voltage limiter transistor 221) with some attenuation and therebyprovide one of several bias sources for the gates of the middletransistors.

The first middle transistor gate is also coupled to the bias voltage viaan RC circuit including a resistor 262 coupled between the first middletransistor gate and the bias voltage and a capacitor 272 coupled betweenthe first middle transistor gate and the ground voltage. The resistor262 and capacitor 272 may be chosen to provide sufficient attenuation ofthe amplified RF signal (the output signal) that will be present due tothe gate-drain and gate-source capacitance of the first middletransistor 213.

The second middle transistor gate is also coupled to the bias voltagevia a RC circuit including a resistor 261 coupled between the secondmiddle transistor gate and the bias voltage and a capacitor 271 coupledbetween the first middle transistor gate and the ground voltage. Theresistor 261 and capacitor 271 may be chosen to remove any AC componentand provide a DC bias voltage to the second middle transistor 212. Inparticular, where the capacitor 272 has a first capacitance and thecapacitor 271 has a second capacitance, the second capacitance may belarger than the first capacitance.

FIG. 3 shows an example plot of the voltages at the drains of thetransistors 211-214 of FIG. 2 over time when the amplified RF signal isgreater than 10 volts. The voltage at the input transistor drain isshown by a first curve M30D, the voltage at the second middle transistordrain is shown by a second curve M31D, the voltage at the first middletransistor drain is shown by a third curve M32D, and the voltage at theoutput transistor drain is shown by a fourth curve M33D. As shown inFIG. 3, the differences between the drain voltages (and thus, thesource-drain voltages M0, M1, M4 are each below 3 volts andapproximately equal.

FIG. 4 shows an example plot of the voltages at the drains of thetransistors 211-214 of FIG. 2 over time when the amplified RF signal isbelow 8.5 volts. As in FIG. 3, the voltage at the input transistor drainis shown by a first curve M30D, the voltage at the second middletransistor drain is shown by a second curve M31D, the voltage at thefirst middle transistor drain is shown by a third curve M32D, and thevoltage at the output transistor drain is shown by a fourth curve M33D.As shown in FIG. 4, the differences between the drain voltages (andthus, the source-drain voltages M0, M2, M4 are each below 3 volts andapproximately equal. Further, the source-drain voltages M0, M2, M4 areless in FIG. 4 than in FIG. 3.

FIG. 5 shows that, in some implementations, a power amplification system500 can include multiple voltage limiters. The power amplificationsystem 500 includes five transistors 511-514 in a cascode arrangement.Whereas the power amplification system 200 of FIG. 2 includes two middletransistors 212-213, the power amplification system 500 of FIG. 5includes three middle transistors 512-514. In various implementations, apower amplification system can include any number of middle transistors,such as zero, one, two (as in FIG. 2), three, (as in FIG. 5), four, ormore.

The power amplification system 500 of FIG. 5 includes an inputtransistor 511 having an input transistor gate configured to receive aradio-frequency (RF) signal, an input transistor source coupled to aground voltage, and an input transistor drain. Coupled to the inputtransistor gate is an input bias circuit 550 configured to provide abias voltage that places the input transistor 511 into an active mode.Although not shown, such an input bias circuit can also be implementedin the power amplification system 200 of FIG. 2.

The power amplification system 500 further includes an output transistor515 having an output transistor drain configured to output an amplifiedversion of the RF signal, an output transistor gate coupled to a biasvoltage (Bias0), and an output transistor source. The output transistordrain is coupled to a supply voltage (Vcc) via an inductor 551. Theoutput transistor drain is also coupled to an output match circuit 540configured to provide impedance matching functionality for the poweramplification system 500. The output matching circuit 540 can, forexample, be a low-pass/low-pass Class E output matching circuit.Although not shown, such an output matching circuit can also beimplemented in the power amplification system 200 of FIG. 2.

The power amplification system 500 further includes a high voltagelimiter coupled between the output transistor drain and outputtransistor gate. As noted above, the high voltage limiter is configuredto prevent a gate-drain voltage of the output transistor 515 fromexceeding a high voltage threshold, e.g., a breakdown voltage of theoutput transistor 515. As also noted above, in many implementations, asingle high voltage limiter transistor and the connection of the outputtransistor gate and gates of the middle transistors 512-514 issufficient to prevent the gate-drain voltage of the middle transistors512-514 from exceeding a breakdown voltage. However, in otherimplementations (e.g., as shown in FIG. 5), the high voltage limiterincludes multiple high voltage limiter transistors.

For example, the power amplification system 500 of FIG. 5 includes afirst high voltage limiter transistor 521 having a first high voltagelimiter transistor gate coupled to the output transistor drain, a firsthigh voltage limiter transistor drain coupled to the output transistordrain, and a first high voltage limiter transistor source coupled to theoutput transistor gate. When the voltage between the output transistordrain (the output signal) and the output transistor gate approaches orexceeds a high voltage threshold, the first high voltage limitertransistor 521 feeds back the output signal to the output transistorgate. The power amplification system 500 further includes a second highvoltage limiter transistor 522 having a second high voltage limitertransistor gate coupled to a middle transistor drain, a second highvoltage limiter transistor drain coupled to a middle transistor drain,and a second high voltage limiter transistor source coupled to a middletransistor gate. When the voltage between the middle transistor drainand the middle transistor gate approaches or exceeds a high voltagethreshold, the second high voltage limiter transistor 521 feeds voltageto the middle transistor gate.

The power amplification system 500 also includes a low voltage limitercoupled between the supply voltage and one or more middle transistorgates. As noted above, the low voltage limiter configured to prevent thegate voltage of the middle transistors from dropping below a low voltagethreshold. As also noted above, in many implementations, a single lowvoltage limiter transistor and the connection of the gates of the middletransistors 512-514 is sufficient to prevent the gate-drain voltage ofthe middle transistors 512-514 from dropping below a low voltagethreshold. However, in other implementations (e.g., as shown in FIG. 5),the low voltage limiter includes multiple low voltage limitertransistors.

For example, the power amplification system 500 of FIG. 5 includes afirst low voltage limiter transistor 531 having a first low voltagelimiter transistor source coupled to a first middle transistor gate, afirst low voltage limiter transistor drain coupled to the supplyvoltage, and a first low voltage limiter transistor gate coupled to afirst supplemental bias voltage (Bias1). The power amplification system500 further includes a second low voltage limiter transistor 532 havinga second low voltage limiter transistor source coupled to a secondmiddle transistor gate, a second low voltage limiter transistor draincoupled to the supply voltage, and a second low voltage limiter gatecoupled to a second supplemental bias voltage (Bias2). In someimplementations, the first supplemental bias voltage and the secondsupplemental bias voltages are identical. For example, a singlesupplemental bias source can be coupled to both the first low voltagelimiter transistor gate and the second low voltage limiter transistorgate. In other implementations, the second supplemental bias voltage isgreater than (or less than) the first supplemental bias voltage.

The power amplification system 500 can include RC circuits (not shown)between the bias voltage and the gates of the middle transistors 512-514and output transistor 515 as described above with respect to the poweramplification system 200 of FIG. 2.

FIG. 6 shows a flowchart representation of a method 600 of amplifying anRF signal. In some implementations (and as detailed below as anexample), the method 600 is at least partially performed by a poweramplification system, such as the power amplification system 200 of FIG.2. In some implementations, the method 600 is at least partiallyperformed by processing logic, including hardware, firmware, software,or a combination thereof. In some implementations, the method 600 is atleast partially performed by a processor executing code stored in anon-transitory computer-readable medium (e.g., a memory).

The method 600 begins, at block 610, with the power amplification system610 receiving an RF signal at a gate of an input transistor. At block620, the power amplification system emits an amplified version of the RFsignal from a drain of an output transistor. At block 630, the poweramplification system dynamically biases the voltage on the gate of theoutput transistor based on the amplified version of the RF signal.

In some implementations, dynamically biasing the voltage on the gate ofthe output transistor further includes dynamically biasing the voltageon the gate of one or more middle transistors. In some implementations,dynamically biasing the voltage on the gate of the output transistorincludes providing a feedback signal from the drain of the outputtransistor to the gate of the output transistor. In someimplementations, dynamically biasing the voltage on the gate of theoutput transistor includes limiting a voltage between the drain of theoutput transistor and the gate of the output transistor. In someimplementations, dynamically biasing the voltage on the gate of theoutput transistor further includes limiting a voltage between the drainof a middle transistor and a gate of a middle transistor.

In some implementations, the feedback signal from the drain of theoutput transistor to the gate of the output transistor is provided by ahigh voltage limiter transistor coupled between the drain of the outputtransistor and the gate of the output transistor. In someimplementations, the feedback signal is provided without a use of anytransformer or balun.

FIG. 7 shows that in some embodiments, some or all of the configurations(e.g., those shown in FIGS. 2 and 5) can be implemented, wholly orpartially, in a module. Such a module can be, for example, a front-endmodule (FEM). In the example of FIG. 7, a module 700 can include apackaging substrate 702, and a number of components can be mounted onsuch a packaging substrate 702. For example, an FE-PMIC component 704, apower amplifier assembly 706 (which can include a voltage limiter 707),a match component 708, and a multiplexer assembly 710 can be mountedand/or implemented on and/or within the packaging substrate 702. Othercomponents such as a number of SMT devices 714 and an antenna switchmodule (ASM) 712 can also be mounted on the packaging substrate 702.Although all of the various components are depicted as being laid out onthe packaging substrate 702, it will be understood that somecomponent(s) can be implemented over other component(s).

In some implementations, a device and/or a circuit having one or morefeatures described herein can be included in an RF electronic devicesuch as a wireless device. Such a device and/or a circuit can beimplemented directly in the wireless device, in a modular form asdescribed herein, or in some combination thereof. In some embodiments,such a wireless device can include, for example, a cellular phone, asmart-phone, a hand-held wireless device with or without phonefunctionality, a wireless tablet, etc.

FIG. 8 depicts an example wireless device 800 having one or moreadvantageous features described herein. In the context of a modulehaving one or more features as described herein, such a module can begenerally depicted by a dashed box 700, and can be implemented as, forexample, a front-end module (FEM).

Referring to FIG. 8, power amplifiers (PAs) 820 can receive theirrespective RF signals from a transceiver 810 that can be configured andoperated in known manners to generate RF signals to be amplified andtransmitted, and to process received signals. The transceiver 810 isshown to interact with a baseband sub-system 808 that is configured toprovide conversion between data and/or voice signals suitable for a userand RF signals suitable for the transceiver 810. The transceiver 810 canalso be in communication with a power management component 806 that isconfigured to manage power for the operation of the wireless device 800.Such power management can also control operations of the basebandsub-system 808 and the module 700.

The baseband sub-system 808 is shown to be connected to a user interface802 to facilitate various input and output of voice and/or data providedto and received from the user. The baseband sub-system 808 can also beconnected to a memory 804 that is configured to store data and/orinstructions to facilitate the operation of the wireless device, and/orto provide storage of information for the user.

In the example wireless device 800, outputs of the PAs 820 are shown tobe matched (via respective match circuits 822) and routed to theirrespective diplexers 824. Such amplified and filtered signals can berouted to an antenna 816 (or multiple antennas) through an antennaswitch 814 for transmission. In some embodiments, the diplexers 824 canallow transmit and receive operations to be performed simultaneouslyusing a common antenna (e.g., 816). In FIG. 8, received signals areshown to be routed to “Rx” paths (not shown) that can include, forexample, a low-noise amplifier (LNA).

A number of other wireless device configurations can utilize one or morefeatures described herein. For example, a wireless device does not needto be a multi-band device. In another example, a wireless device caninclude additional antennas such as diversity antenna, and additionalconnectivity features such as Wi-Fi, Bluetooth, and GPS.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled”, as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Additionally, the words “herein,” “above,” “below,” and words of similarimport, when used in this application, shall refer to this applicationas a whole and not to any particular portions of this application. Wherethe context permits, words in the above Description using the singularor plural number may also include the plural or singular numberrespectively. The word “or” in reference to a list of two or more items,that word covers all of the following interpretations of the word: anyof the items in the list, all of the items in the list, and anycombination of the items in the list.

The above detailed description of embodiments of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whileprocesses or blocks are presented in a given order, alternativeembodiments may perform routines having steps, or employ systems havingblocks, in a different order, and some processes or blocks may bedeleted, moved, added, subdivided, combined, and/or modified. Each ofthese processes or blocks may be implemented in a variety of differentways. Also, while processes or blocks are at times shown as beingperformed in series, these processes or blocks may instead be performedin parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

While some embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

What is claimed is:
 1. A power amplification system comprising: a signalinput terminal configured to receive an input signal; a signal outputterminal configured to provide an amplified signal; a supply voltageterminal configured to receive a supply voltage; one or more biasterminals configured to receive one or more bias voltages; a signalamplifier configured to amplify the input signal and coupled to thesignal input terminal, the signal output terminal, the supply voltageterminal, and the one or more bias terminals, the signal amplifierhaving a plurality of transistors biased by the one or more biasvoltages including an input transistor, an output transistor, and one ormore middle transistors; a voltage limitation system configured to limitvoltages across one or more of the plurality of transistors, the voltagelimitation system including a high voltage limiter configured to preventvoltages from exceeding a high voltage threshold and a low voltagelimiter configured to prevent voltages from dropping below a low voltagethreshold; and an input bias circuit coupled to the one or more biasterminals and configured to provide a bias signal to the inputtransistor.
 2. The power amplification system of claim 1 wherein thehigh voltage limiter is configured to prevent voltages across the outputtransistor from exceeding a breakdown voltage of the output transistor.3. The power amplification system of claim 2 wherein the low voltagelimiter is configured to prevent voltages at a gate of a middletransistor of the plurality of middle transistors from dropping below abias voltage that places the middle transistor in an active mode.
 4. Thepower amplification system of claim 1 further comprising an output matchcircuit coupled to the signal output terminal and the output transistor.5. The power amplification system of claim 1 wherein the plurality oftransistors is arranged in a cascode configuration.
 6. The poweramplification system of claim 5 wherein the input transistor is coupledto the input signal terminal and the one or more middle transistors. 7.The power amplification system of claim 6 wherein the output transistoris coupled to the output signal terminal and the one or more middletransistors.
 8. The power amplification system of claim 1 wherein theplurality of transistors comprise metal-oxide-semiconductor field-effecttransistors.
 9. The power amplification system of claim 1 wherein theoutput transistor is coupled to the supply voltage terminal through aninductor.
 10. The power amplification system of claim 1 wherein the highvoltage limiter is configured to generate a feedback signalcorresponding to the amplified signal, the feedback signal beingprovided to the output transistor and to a transistor of the one or moremiddle transistors to provide one of several bias sources to preventgate-drain voltages from exceeding a breakdown voltage.
 11. The poweramplification system of claim 1 wherein the low voltage limiter isconfigured to feed the supply voltage to a middle transistor of the oneor more middle transistors to provide one of several bias sources toprevent a gate voltage at the middle transistor from dropping below abias voltage that places the middle transistor in an active mode.
 12. Afront-end module comprising: a packaging substrate configured to receivea plurality of components; and a power amplifier assembly implemented onthe packaging substrate, the power amplifier assembly including aplurality of power amplifiers configured to generate a plurality ofamplified signals, individual power amplifiers including a signal inputterminal configured to receive an input signal and a signal outputterminal configured to provide an amplified signal; individual poweramplifiers also including a supply voltage terminal configured toreceive a supply voltage and one or more bias terminals configured toreceive one or more bias voltages; individual power amplifiers alsoincluding a signal amplifier configured to amplify the input signal andcoupled to the signal input terminal, the signal output terminal, thesupply voltage terminal, and the one or more bias terminals, the signalamplifier having a plurality of transistors biased by the one or morebias voltages including an input transistor, an output transistor, andone or more middle transistors; individual power amplifiers alsoincluding a voltage limitation system configured to limit voltagesacross one or more of the plurality of transistors, the voltagelimitation system including a high voltage limiter configured to preventvoltages from exceeding a high voltage threshold and a low voltagelimiter configured to prevent voltages from dropping below a low voltagethreshold; and an input bias circuit coupled to the one or more biasterminals and configured to provide a bias signal to the inputtransistor.
 13. The front-end module of claim 12 wherein the packagingsubstrate includes a silicon-on-insulator (SOI) substrate.
 14. Thefront-end module of claim 12 wherein the input transistor and outputtransistor comprise complementary metal-oxide semiconductor (CMOS)transistors.
 15. The front-end module of claim 12 further comprising anantenna switch module configured to receive the plurality of amplifiedsignals.
 16. The front-end module of claim 12 further comprising a matchcomponent having a plurality of output match circuits coupled tocorresponding output transistors of the plurality of power amplifiers.17. A wireless device comprising: a transceiver configured to generate aradio-frequency (RF) signal; a front-end module (FEM) in communicationwith the transceiver, the FEM including a packaging substrate configuredto receive a plurality of components, the FEM further including a poweramplification system implemented on the packaging substrate andconfigured to generate an amplified RF signal for transmission, thepower amplification system including a plurality of power amplifiersindividually configured to amplify signals, individual power amplifiersincluding a signal input terminal configured to receive an input signaland a signal output terminal configured to provide an amplified signal;individual power amplifiers also including a supply voltage terminalconfigured to receive a supply voltage and one or more bias terminalsconfigured to receive one or more bias voltages; individual poweramplifiers also including a signal amplifier configured to amplify theinput signal and coupled to the signal input terminal, the signal outputterminal, the supply voltage terminal, and the one or more biasterminals, the signal amplifier having a plurality of transistors biasedby the one or more bias voltages including an input transistor, anoutput transistor, and one or more middle transistors; and individualpower amplifiers also including a voltage limitation system configuredto limit voltages across one or more of the plurality of transistors,the voltage limitation system including a high voltage limiterconfigured to prevent voltages from exceeding a high voltage thresholdand a low voltage limiter configured to prevent voltages from droppingbelow a low voltage threshold; and an antenna in communication with theFEM, the antenna configured to transmit the amplified RF signal receivedfrom the power amplification system.
 18. The wireless device of claim 17further comprising a plurality of match circuits coupled tocorresponding output transistors of the plurality of power amplifiers.19. The wireless device of claim 17 further comprising an input biascircuit configured to provide bias signals to the input transistors.